The U.S. Navy, through the Navy Metalworking Center (www.nmc.ctc.com), is now working on a project to use electron beam welding as a replacement for traditional welding in the fabrication of first reduction gears on Virginia Class submarines.

The goal is to reduce manufacturing costs while improving the quality of the welds on the submarines, and if successful the project team will seek other potential uses on the submarines and other naval weapons systems.

The current welding processes used in the manufacture of a reduction gear requires multiple passes in complex sequence with some joints requiring double-sided welding to ensure full penetration.

The 14-month project is expected to reduce fabrication time by incorporating single-pass, full-penetration welds; utilize narrow welds that improve fit-up and simplify machining operations on fabricated gears by reducing rim-to-shaft distortion; eliminate the need for closing plates on gear fabrication; and reduce Magnetic Particle Testing requirements due to single-sided welds.

Electron beam welding is a fusion joining process that was first introduced commercially in 1959. It uses a special electron beam gun that emits a highly energized stream of electrons which can be focused onto a welding joint with control over weld width, penetration and heat generation.

As the electrons strike the workpiece, their energy is converted into heat which instantly vaporizes the metal with temperatures reaching nearly 25,000 degrees C.

The heat penetrates deeply, making it possible to weld much thicker workpieces than is possible with other welding techniques. But because the beam is tightly focused, the total amount of heat imparted to the workpiece is usually lower than traditional arc welding methods. This results in lower material distortion.

The process is done in a vacuum that greatly reduces weld contamination. Filler material us usually not used, and weld ratios can be as high as 20-to-1 depth-to-width compared to the normal ratio of 2-to-1 of tungsten inert gas welding.

Welds can be as narrow as a few thousandths of an inch or wider than a quarter of an inch, and dissimilar materials can be effectively welding using this technique.

The technique does have limitations such as high equipment costs, work chamber size limitations, higher weld preparation costs than traditional welding, x-rays are produced that require additional safety precautions be taken, and rapid solidification rates can cause cracking in some materials, especially high carbon steels.

Until a few years ago electron beam welding was primarily a manual operation that required an operator to focus the invisible beam using a surrogate block of refractory metal and heating a spot on the metal to white hot.

The focus then was adjusted until the spot's optical brightness appeared to be at its sharpest. Recent developments, however, have used computed tomography, creating images by sections or sectioning, to automate the focusing process and produce welds that can be consistently reproduced.

A device called an EBeam Profiler developed by Lawrence Livermore Scientist John Elmer and Electrical Engineer Alan Teruya allows an operator to quantify the electron beam's power-density distribution, determine its sharp focus and correlate machine settings with beam properties.

Using this tool, engineers can precisely reproduce an electron beam on the same machine time and again. This has reduced the costs of the high-value electron beam welds and made their use more widely available.

Chicago-based Sciaky, Inc. (www.sciaky.com) has licensed and sells this technology under the name EBeam 20/20 Profiler.

It is not easy for people who have never worked in a shipyard to understand how enormous the task of building a warship it. LPD 21, the New York, is 684 feet long. If it were stood on its end it would be taller than a 60-story building, but unlike a building the ship does not stay in one place. It not only has to move with purpose from place to place, it has to do it in all sorts of weather and sea conditions.

It is not as simple a construct as a 60-story building. While most buildings are basically rectangular, slab-sided structures a ship is all curves shaped to enable it to move more easily through the water. Not only does it have all the plumbing, heating, ventilation and other utility systems that a building has, but it also has its own propulsion and power generating systems. While a building most cope with wind and rain, sleet and snow, a ship must cope with all of that plus ever-present, corrosive saltwater and things that try to tear the ship's hull open such as underwater rocks and reefs and, in times of war, the occasional torpedo of underwater mine.

While the metal framework of a building is often welded in addition to being riveted, most of the rest of the structure is bolted onto the framework. On a ship everything is either welded together or attached to the ship with a weld because a ship, unlike a building, “works”. It bends and twists in several directions at the same time in response to varying water pressure on the hull. A building might “move” if there is an earthquake, but a ship moves all of the time it is at sea.

Compared to building a ship, all other constructions become simple, and that makes building a ship like no other job in the world.